1. A Review of Cyclic Testing Protocols for Flexor Tendon Repairs
Min Kai Chang1, Zeus Yiwei Lim2, Yoke Rung Wong2, Shian Chao Tay1,2,3
Duke-NUS Medical School
Biomechanics Laboratory, Singapore General Hospital
3. Department of Hand Surgery, Singapore General Hospital
INTRODUCTION
MATERIALS AND METHODS
CYCLIC TESTING VS STATIC TESTING
LITERATURE SEARCH
Searches with PubMed on National Centre for Biotechnology Information (NCBI)
Adhered to Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines
Differences between 2 in-vitro methods
Differences
Static load-to-failure test
Cyclic test
What it involves
Constant rate of displacement with increasing force applied
Repetitive application and removal of load
Pros
Less time to perform
Simulate post-op rehab
Gap formation at lower loads (more rigorous)
Cons
Does not simulate post-op rehab
Many different protocols in literature with no standards
DEFINITIONS OF PARAMETERS IN A PROTOCOL
CYCLIC TESTING PROTOCOL: Procedure that subjects a group of repaired flexor tendons to repetitive loading using parameters below\
FREQUENCY (Hz): Number of cycles over time
DISPLACEMENT RATE (mm/min): Change in length between apparatus holding tendons over time
SINGLE-STAGED: Protocols that use only one set of the above parameters
MULTIPLE-STAGED: Protocols that use increasing cyclic loads sequentially
PRELOAD
CYCLIC LOAD
1 CYCLE
PRELOAD (N): Minimum load
CYCLIC LOAD (N): Maximum load
NUMBER OF CYCLES: Number of repetitions during the protocol
Cyclic testing is better to evaluate flexor tendon repairs, but no standard protocol
OBJECTIVES
1. Provide an overview of reported protocols for cyclic testing of flexor tendon repairs
2. Propose parameters used for cyclic testing to reflect post-op rehab protocols
RESULTS AND DISCUSSION
LITERATURE SEARCH
PRELOAD
Proposed: 2N
Reason: Simulate resting tension of tendons after repair (1N for healthy FDS tendon, higher for repaired tendons) (Bright and Urbaniak, 1976; Tang, 2007)
2096 studies using keyword “flexor tendon repair”
Include keyword “cyclic test”
36 studies after keywords search
Exclude 7 studies with no parameters
29 studies with cyclic testing parameters
Exclude 14 duplicates
15501 studies using keyword “cyclic test”
Include keyword “flexor tendon repair”
44 studies after keywords search
Exclude 28 studies with no parameters
16 studies with cyclic testing parameters
31 studies with cyclic testing parameters
Include 8 studies using references of the above studies
39 studies after secondary search
35 studies with 42 protocols
(29 studies with 1 protocol, 5 studies with 2 protocols, and 1 study with 3 protocols)
Exclude 4 studies with exact same protocols
CYCLIC LOAD
Proposed: 15N for passive mobilization, 38N for active mobilization
Reason: Derived from studies of in vivo forces of healthy flexor tendons AND increase in loads of up to 50% in repaired tendons
NUMBER OF CYCLES
Proposed: 2000 cycles
Reason: Derived from number of repetitions of exercises in post-op rehab protocol (10 flexion-extension exercises per hour daily for first 4 weeks, 10 hours per day) (Edsfeldt et al., 2015; Kursa et al., 2006; Strickland, 1999)
FREQUENCY
Proposed: 0.2Hz
Reason: 10 flexion-extension exercises can typically be performed within 1 minute, yielding a frequency of 0.2Hz (Matheson et al., 2005)
DISPLACEMENT RATE
Proposed: 100 mm/min for passive mobilization, 135mm/min for active mobilization
Reason: 10 flexion-extension exercises per minute AND passive flexion involves inter-tendinous excursion of approximately 10mm, while active flexion involves inter-tendinous excursion of 13.5mm (Sapienza et al., 2013)
DISTRIBUTION OF PARAMETERS IN PROTOCOLS
OUTCOME MEASUREMENTS
Proposed: 1) Number of cycles to reach 2-3mm gap, 2) Magnitude of gap after cycling, 3) Mode of failure (suture pullout or breakage)
Reason: 2-3mm gap was found to increase gliding resistance, adhesion formation, risk of rupture (Zhao et al., 2004)
CONCLUSIONS
CYCLIC TESTING FOR FLEXOR TENDON REPAIRS
This review highlights the disparity in cyclic testing for flexor tendons and consolidates the current understanding of cyclic testing
We propose two single-staged protocols for cyclic testing
Protocol 1 is designed to simulate passive rehabilitation, with a cyclic load of 15N, preload of 2N, number of cycles of at least 2000, and frequency of 0.2Hz
Protocol 2 is designed to simulate active rehabilitation, with a cyclic load of 38N, preload of 2N, number of cycles of at least 2000, and frequency of 0.2Hz
6. Matheson G, Nicklin S, Gianoutsous MP, Walsh WR. Comparison of zone II flexor tendon repairs using an in vitro linear cyclic testing protocol. Clin Biomech (Bristol, Avon). 2005;20(7):
7. Sapienza A, Yoon HK, Karia R, Lee SK. Flexor tendon excursion and load during passive and active simulated motion: a cadaver study. The Journal of hand surgery, European volume. 2013;38(9):
8. Zhao C, Amadio PC, Tanaka T, et al. Effect of gap size on gliding resistance after flexor tendon repair. J Bone Joint Surg Am. 2004;86-A(11):
This work was supported by the Duke-NUS Medical School, Musculoskeletal Sciences Academic Clinical Program (AM-ETHOS01/FY2016/28-A31), SingHealth Medical Student Talent Development Award-Project (FY2017 Cycle 1), Surgery Academic Clinical Program grant (Biomechanics Lab Programme), and the Singapore Ministry of Health’s National Medical Research Council under its Center Grant (NMRC/CG/M011/2017)
References:
1. Bright DS, Urbaniak JS. Direct measurements of flexor tendon tension during active and passive digit motion and its application to flexor tendon surgery. Trans Orthop Res Soc. 1976;240.
2. Tang JB. Indications, methods, postoperative motion and outcome evaluation of primary flexor tendon repairs in Zone 2. J Hand Surg Eur Vol. 2007;32(2):
3. Edsfeldt S, Rempel D, Kursa K, Diao E, Lattanza L. In vivo flexor tendon forces generated during different rehabilitation exercises. J Hand Surg Eur Vol. 2015;40(7):
4. Kursa K, Lattanza L, Diao E, Rempel D. In vivo flexor tendon forces increase with finger and wrist flexion during active finger flexion and extension. J Orthop Res. 2006;24(4):
5. Strickland JW. Flexor Tendon - Acute Injuries. Philadelphia: Churchill Livingstone; 1999